(i) Field of the Invention
The present invention relates to the use of a system constituted by a strongly acidic ion-exchange resin as catalyst and a (co)oligomerization additive, as a catalytic ring-opening lactide and glycolide (co)oligomerization system. The present invention also relates to a lactide and glycolide (co)oligomerization method comprising the use of such a catalytic system.
(ii) Description of Related Art
Nowadays, increasing attention is given to synthetic polymers for the production of artificial organs and the formulation of medicaments [Chem. Eng. News 2001, 79 (6), 30]. The polymers concerned must meet a certain number of criteria and, in particular, they must be biocompatible. The biodegradable characteristic is an additional advantage if the polymer must be eliminated after an appropriate period of implantation in an organism. In this regard, the copolymers based on lactic and glycolic acid (PLGA) are of great interest because they are sensitive to hydrolysis and are degraded in vivo with the release of non-toxic by-products. The field of application of the PLGA's is very wide (Adv. Mater. 1996, 8, 305 and Chemosphere 2001, 43, 49). In the surgical field, they are used for the synthesis of multistrand threads, sutures, implants, prostheses, etc. In pharmacology, they allow the encapsulation, the transfer and the controlled release of active ingredients.
For all these applications, the key factor is the rate of degradation of the PLGA which of course depends on their structure (chain length, dispersity, proportion, stereochemistry and chain formation of monomers, etc). In recent years, numerous works have therefore targeted the development of catalysts and/or promoters of (co)polymerization, i.e. for polymerization or copolymerization, of lactide and glycolide allowing the preparation of PLGA with a controlled structure.
The use of metal systems usually leads to a contamination of the copolymers thus obtained through the presence of metallic salts, which sometimes constitutes a serious limitation depending on the envisaged applications. The development of non-metal systems allowing the controlled (co)polymerization of lactide and glycolide is therefore a significant issue. The present invention fits into this category and relates more particularly to low-mass lactide and glycolide (co)polymers, i.e. lactide and glycolide (co)oligomers.